This invention relates to a tanker, particularly to a cargo tank which is cylindrical and rotatable about a horizontal axis and has a torque partition member dividing it into independent upper and lower compartments whereby when a liquid is unloaded from the lower compartment, another liquid can be loaded in the upper compartment and the loaded upper compartment can be changed to the lower level position by the rotation of the tank which is caused by a torque produced by the partition member during loading and unloading.
A tanker transferring crude oil typically includes compartmented tanks for carrying crude oil exclusively and holding ballast water. Since such a tanker carries no cargo on its return passage, it should be provided with ballast water for the stability of the tanker. Therefore, it is not economical.